Conventional handheld radiotelephones provide alert signals to a user for an incoming call, using two different mechanisms. A first type of alert is provided as a mechanical ringing sound (referred to herein as “ringing”), using an off electronic signalling device, such as a buzzer or loudspeaker. This mechanical ringing is provided in different cadences and with different loudness levels so that a user can select and fix a cadence and a sound intensity preferred by that user. A second type of alert is provided by mechanical vibration using, for example, an electromechanical vibrator that is embedded in the radiotelephone. A vibrator mechanically vibrates the entire radiotelephone in communicating an alert signal and thus provides a relatively silent or unobtrusive alert signal. By contrast, ringing is used to communicate a relatively obtrusive, non-silent alert signal. Most users choose, or accept, a ringing alert for most purposes, except where a meeting or similar event is occurring. A ringing alert signal may be a conventional signal with a unique set of cadences, a sequence of one or more musical notes, or a similar signal.
Conventional radiotelephones made by a single vendor, or manufactured according to closely related models, often provide (nearly) identical ringing alert signals. As such, in a group of adjacent radiotelephone users, it is sometimes difficult to determine whose device is actually ringing for an incoming call: each of two or more radiotelephone users reaches for and attempts to activate his or her radiotelephone at the same time in response to the incoming call. Identifying whose radiotelephone is actually responding to the incoming call requires greater attention to detail and more careful listening by radiotelephone users in such a group. Further, presence of the mechanical ringing often disturbs others who are not part of the fraternity of habitual radiotelephone users.
Another issue with use of ringing alert signals for a conventional radiotelephone is that, once the loudness or sound intensity is selected by the user, that sound level is fixed for all environments, until the user takes the trouble to change the sound level. A selected (and fixed) sound level may be too low in a noisy environment and may be too high and intrusive in an intimate, low key environment.
What is needed is a radiotelephone that provides a unique and easily distinguishable alert signal, such as a distinguishable human voice that is easily recognized by the targeted user and by other radiotelephone users whose devices are not presently receiving an incoming call notification. Preferably, the initial sound intensity and the subsequent sound intensity for this distinguishable alert (“DA”) signal will vary automatically according to (i) noise level in the local environment and (ii) estimated distance of the user from the device when the incoming call is received.